In a prior-art optical disk apparatus, when information recorded on an optical disk is reproduced by an optical pickup or when information is recorded on an optical disk by the optical disk, the optical axis of a laser beam from the optical pickup is set so as to be perpendicular to the recording face of the optical disk. If the optical axis of the laser beam tilts with respect to the recording face of the optical disk, there is a problem of being unable to accurately carry out recording or reproducing on the optical disk. Conventionally, various tilt adjustment mechanisms for adjusting the tilt of the optical axis are provided for optical disk apparatuses. In particular, high-density optical disks have become to be used, since optical apparatuses have been made higher in speed and larger in capacity in recent years, whereby the accuracy of recording/reproducing has become requested to be strict. Hence, the tilt adjustment mechanism for adjusting the relative angle between the optical axis of the optical pickup and the optical disk has become an important mechanism. Furthermore, since the optical disk apparatus is earnestly requested for reduction in profile, a compact head capable of meeting the need for the reduction in profile has begun to be used; hence the tilt adjustment mechanism is also requested to be capable of meeting the need for further reduction in profile.
In response to such requests for higher speed, larger capacity and lower profile in optical disk apparatuses, various tilt adjustment mechanisms have been developed. As prior-art tilt adjustment mechanisms, devices disclosed in Japanese Unexamined Patent Publication No. Hei 9-320214 and Japanese Unexamined Patent Publication No. Hei 10-208372 are available, for example.
FIG. 14 is a plan view showing a tilt adjustment mechanism in an optical disk apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 9-320214. In FIG. 14, an optical pickup 102 for emitting laser beam to an optical disk 101 is installed between a first guide shaft 103 and a second guide shaft 104 being adjusted in advance so as to be parallel with each other. A first adjustment member 105A and a second adjustment member 105B are provided at both ends of the first guide shaft 103. A third adjustment member 105C and a support member 106 are provided at both ends of the second guide shaft 104. The first to third adjustment members 105A, 105B and 105C are provided with rotation members 108A, 108B and 108C being rotatable with respect to the chassis and also provided with cams 109A, 109B and 109C protruding on the upper faces of these rotation members 108A, 108B and 108C and serving as bearings for the first guide shaft 103 or the second guide shaft 104. These cams 109A, 109B and 109C are configured so that their heights change gradually depending on the rotation angles of the rotation members 108A, 108B and 108C. Hence, by rotating the rotation members 108A, 108B and 108C, the cams 109A, 109B and 109C are rotated, whereby the ends of the first guide shaft 103 and the second guide shaft 104, corresponding thereto respectively, are moved up and down.
In addition, in the vicinities of the rotation members 108A, 108B and 108C, the vicinities of the ends of the first guide shaft 103 and the second guide shaft 104 are supported by U-shaped fittings 107A, 107B and 107C secured to the chassis so as to be movable only upward. Furthermore, the vicinities of the ends of the first guide shaft 103 and the second guide shaft 104 are pressed downward elastically by pressure springs 110A, 110B and 110C. Moreover, the support member 106 rotatably supports one end of the second guide shaft 104.
In the prior-art optical disk apparatus configured as described above and disclosed in Japanese Unexamined Patent Publication No. Hei 9-320214, the rotation members 108A, 108B and 108C and the cams 109A, 109B and 109C, serving as adjustment members, are formed to have the same shapes, respectively. Hence, by rotating the rotation members 108A, 108B and 108C by the same angle, the support points corresponding to the first guide shaft 103 and the second guide shaft 104 are configured so as to be moved by the same height. For this reason, the components of the adjustment members 105A, 105B and 105C are required to be made with high accuracy. The distortion and tilt of the plane including the center axis of the first guide shaft 103 and the center axis of the second guide shaft 104 are adjusted by using the three adjustment members 105A, 105B and 105C.
In other words, in the tilt adjustment of this prior-art optical disk apparatus, it is necessary to adjust the movement face of the optical pickup 102 while the parallelism between the center axis of the first guide shaft 103 and the center axis of the second guide shaft 104 is maintained at all times. Therefore, the parallelism between the center axis of the first guide shaft 103 and the center axis of the second guide shaft 104 is adjusted in advance, and the adjustment members 105A and 105B are moved synchronously by the same amount, and then the adjustment members 105B and 105C are moved synchronously by the same amount. By repeating these adjustment operations, the optical pickup 102 is disposed so as to take an optimal movement path. Hence, in this prior-art optical disk apparatus, synchronous adjustment processes at a plurality of points are required a plurality of times so that the recording face of the optical disk 101 becomes parallel with the movement face of the optical pickup 102. In this synchronous adjustment process, two of the plurality of points are required to be rotated and adjusted synchronously; hence, manual adjustment is difficult, whereby it is necessary to use jigs or adjustment devices specially intended for the purpose.
In the prior-art optical disk apparatus configured as described above, the components of the adjustment members of the optical disk apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 9-320214 are required to be made with high accuracy, and special devices are required to be used for the tilt adjustment in the production process thereof. This results in causing a problem of increasing production cost. Since this prior-art optical disk apparatus is configured so that the movement face of the optical pickup is adjusted by using the adjustment members disposed at the three points, the adjustment process is required a plurality of times, whereby complicated adjustment work is necessary. Furthermore, air current produced by the rotation of the optical disk flows through the space in which the optical pickup is disposed, fine-grain dust adheres to the optical components thereof, and the amount of light decreases during a long period of use, thereby causing reduction in performance or falling into impossible reproduction in the worst case.
FIG. 15 is a side sectional view showing the vicinity of the spindle motor installation portion of the prior-art optical disk apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 10-208372. In FIG. 15, a spindle motor 112, the rotation shaft of which is secured to a turntable 111, is installed on the upper face of a support plate 113. A first locking screw 115 passes through a first spring 115A disposed between a locking board 114 for supporting the entire apparatus and the support plate 113 and is threadedly engaged with the threaded portion of the support plate 113. Hence, the support plate 113 is biased by the first spring 115A in the direction of being separated from the locking board 114. In addition, just like the first locking screw 115, a second locking screw 116 passes through a second spring 116A disposed between the locking board 114 and the support plate 113 and is threadedly engaged with the threaded portion of the support plate 113. Hence, the support plate 113 is biased by the second spring 116A in the direction of being separated from the locking board 114. The first locking screw 115 and the second locking screw 116 are provided at positions away from the same distance from the center axis of an optical disk mounted on the turntable 111.
A hemispherical convex portion 117 protruding downward is formed on the lower face of the support plate 113. The hemispherical face of this convex portion 117 is formed on an arc, the center of which is located at a point 111b wherein a disk mounting face 111a is orthogonal to the center of the rotation shaft of the spindle motor 112. On the upper face of the locking board 114, three small hemispherical protrusions 118, protruding upward, are formed. These protrusions 118 are disposed so as to support the hemispherical convex portion 117 at three points.
Next, tilt adjustment work in the apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 10-208372 configured as described above will be described.
First, when the first locking screw 115 threadedly engaged with the support plate 113 is rotated, the support plate 113 is turned and displaced along the shape of the hemispherical convex portion 117. As a result, the spindle motor 112 and the turntable 111 can be tilted in the radial direction of the tracks of the optical disk.
Next, when the second locking screw 116 threadedly engaged with the support plate 113 is rotated, the support plate 113 is turned and displaced along the shape of the hemispherical convex portion 117. As a result, the spindle motor 112 and the turntable 111 can be tilted in the tangential direction of the tracks of the optical disk.
By rotating the first locking screw 115 and the second locking screw 116 as described above, tilt adjustment can be carried out so that the disk mounting face 111a becomes orthogonal to the optical axis of the optical pickup.
In the optical disk apparatus configured as described above and disclosed in Japanese Unexamined Patent Publication No. Hei 10-208372, the spindle motor and the turntable are directly turned with respect to the movement face of the optical pickup during the tilt adjustment operation. Hence, the configuration of this optical disk apparatus is required to secure space for vertical adjustment of the optical disk mounted on the turntable, thereby hindering profile reduction of the apparatus. The optical disk apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 10-208372 is configured so that the spindle motor for rotating the optical disk is supported by the springs 115A and 116A serving as the tilt adjustment members. Because of this configuration, in the case when an unbalanced optical disk is mounted and rotated, the spindle motor portion may resonate, thereby causing a danger of producing vibration, such as swinging, resulting in adversely affecting devices.
Next, specific examples of prior-art tilt adjustment members are taken and their problems will be described.
In an optical disk apparatus, information is recorded by applying laser beam to an optical disk and by changing the state of the optical disk. In addition, recorded information is reproduced on the basis of the difference in the reflection of the laser beam due to the difference in the state of the recording face of the optical disk. Hence, the laser beam emitted from the optical pickup is required to be applied accurately so as to be orthogonal to the recording face of the optical disk without changing the shape of the spot light thereof. Therefore, in the production process of the optical disk apparatus, it is necessary to accurately adjust the application angle of the laser beam to the optical disk while the laser beam emitted from the optical pickup is applied to the recording face of the optical disk. In this adjustment process, the relationship in height between the optical disk mounting face of the turntable rotating with the optical disk mounted thereon (or a chassis rotatably supporting this turntable) and the movement face of the optical pickup by the movement mechanism of the optical pickup (or a sub chassis supporting this movement mechanism) is adjusted. Furthermore, the parallelism between the reference planes of the chassis and the sub chassis is adjusted so as to be within predetermined accuracy in the production process of the optical disk apparatus.
Apparatuses wherein such a relationship in height is required to be adjusted accurately are not limited to optical disk apparatuses. For example, in magnetic recording/reproducing apparatuses, such as video tape recorders (VTRs), the positional relationship between a rotation head drum on which tape serving as a recording medium is wound askew so as to carry out helical recording thereon and the traveling tape, the positional relationships among a plurality of magnetic heads provided inside the rotation head drum relative to the tape, etc. are also required to be adjusted similarly.
The chassis supporting the turntable and the sub chassis supporting the movement mechanism, described above, are generally configured so as to be supported at three points. In the case when the parallelism between the reference plane of the chassis and the reference plane of the sub chassis is adjusted, one of the three support points is used as an engaged movable fulcrum, and the heights (distances) at the other two points are made adjustable, and then the above-mentioned tilt adjustment should be carried out.
FIG. 16 is a sectional view showing the configuration of the adjustment point of a prior-art tilt adjustment mechanism configured as described above. In FIG. 16, the portion (a) shows a state before an adjustment screw 311 is installed in a sub chassis 303 and a chassis 304, and the portion (b) shows a state wherein the adjustment screw 311 has been installed in the sub chassis 303 and the chassis 304.
In FIG. 16, a threaded hole 303a having a female thread 303n into which the adjustment screw 311 is tightened is formed in the sub chassis 303. The chassis 304 is disposed so that its height (separation distance) is adjusted with respect to the sub chassis 303, and the adjustment screw 311 inserted into a through hole 304 formed in the chassis 304 is threadedly engaged with the threaded hole 303a formed in the sub chassis 303. An adjustment spring 314 is disposed in the vicinity of the threaded hole 303a and held between the sub chassis 303 and the chassis 304. Hence, the chassis 304 is biased in the direction of being separated from the sub chassis 303 and locked by the head portion 311a of the adjustment screw 311, whereby the distance (the separation distance) between the chassis 304 and the sub chassis 303 is determined. In this example, the adjustment spring 314 is the so-called helical spring, and the adjustment screw 311 is disposed so as to pass through the helical spring. Hence, a boss portion 303b, in which the threaded hole 303a is formed, is formed to have a diameter slightly smaller than the diameter of the spring so as to be insertable into the helical spring. Because of this configuration, the female thread 303n can be formed so as to be long in the sub chassis 303, whereby the portion tightened by the screw is made long and the assembly work for the adjustment spring 314 is made easy.
The operation of the prior-art tilt adjustment mechanism configured as described above will be described below.
First, the adjustment spring 314 is inserted over the boss portion 303b of the sub chassis 303. Next, the chassis 304 is disposed at a predetermined position, and the adjustment screw 311 is passed through a through hole 304a in the chassis 304 and temporarily screw-locked into the threaded hole 304a in the chassis 304 (turning operation in the arrow direction indicated by letter F in the portion (a) of FIG. 16). Next, the adjustment screw 311 is turned (turning in the arrow directions indicated by letter R in the portion (b) of FIG. 16) so that the adjustment screw 311 is threadedly engaged with the female thread 303n in the threaded hole 303a thereby to adjust the distance between the sub chassis 303 and the chassis 304. By this thread engagement operation, the position of the head portion 311a of the adjustment screw 311 is moved with respect to the sub chassis 303, whereby the position of the chassis 304 (the separation distance: the distance indicated by letter M in the portion (b) of FIG. 16) biased by the adjustment spring 314 so as to be separated is determined.
After the tilt adjustment is completed as described above, the adjustment screw 311 is locked by a screw locking treatment by using locking paint, for example, so as not to rotate, whereby the rotation of the adjustment screw 311 is prevented and the height of the head portion 311a remains unchanged.
However, in the above-mentioned prior-art tilt adjustment mechanism, the female thread 303n is required to be formed in advance at the predetermined position of the boss portion 303b of the sub chassis 303, thereby having a problem of increasing machining cost. In addition, if the backlash between the thread portion 311n of the adjustment screw 311 and the female thread 303n of the boss portion 303b is large, there is a problem of lowering the accuracy of the adjustment. On the other hand, if the clearance is made smaller so that the backlash between the threaded portion 311n of the adjustment screw 311 and the female thread 303n of the boss portion 303b is made smaller, the rotation of the adjustment screw 311 becomes heavy, thereby causing a problem of making the adjustment work difficult. If an attempt is made to suitably set the clearance, variations in the machining accuracy of the female thread 303n of the sub chassis 303 and the quality of the adjustment screw 311 are required to be eliminated.
As a tilt mechanism for solving the problems in the above-mentioned prior-art tilt adjustment mechanism shown in FIG. 16, a mechanism shown in FIG. 17 is available. FIG. 17 is a sectional view showing a tilt adjustment point in another configuration of the prior-art tilt adjustment mechanism. In FIG. 17, the portion (a) shows a state before an adjustment screw 411 is installed in a sub chassis 403 and a chassis 404, and the portion (b) shows a state wherein the adjustment screw 411 has been installed in the sub chassis 403 and the chassis 404.
As shown in FIG. 17, no threaded portion is formed in a through hole 403a in the sub chassis 403, and a tip portion 411t, that is, the tip of the threaded portion 411n of the adjustment screw 411, is formed to have a tapered shape. The adjustment screw 411 shown in FIG. 17 is the so-called tapping screw having a male thread. This adjustment screw 411 is inserted into a through hole 404a in the chassis 404 and temporarily screw-locked to the through hole 403a in the chassis 403 (turning operation in the arrow direction indicated by letter F in the portion (a) of FIG. 17). Next, the adjustment screw 411 is turned (turning in the arrow directions indicated by letter R in the portion (b) of FIG. 17) to adjust the distance between the sub chassis 403 and the chassis 404, while the adjustment screw 411 is engaged with the through hole 403a. By this engagement operation, the position of the head portion 411a of the adjustment screw 411 is moved with respect to the sub chassis 403, whereby the position of the chassis 404 (the separation distance: the distance indicated by letter M in the portion (b) of FIG. 17) biased by the adjustment spring 414 so as to be separated is determined.
By screwing the adjustment screw 411 into the through hole 403a in the sub chassis 403 as described above, the tip portion 411t of the adjustment screw 411 forms a female thread inside the through hole 403a. 
The tilt adjustment mechanism shown in FIG. 17 is characterized in that it is not necessary to form a female thread in the boss portion 403b thereof in advance. However, in the tilt adjustment, since the threaded portion 411n of the adjustment screw 411 reciprocates along the female thread portion, formed by the tapping operation, of the through hole 403a in the sub chassis 403, there is a problem of making the adjustment not easy. In other words, in the tilt adjustment, when the tip portion 411t of the adjustment screw 411 is inserted into the through hole 403a, rotating the adjustment screw 411 becomes very tight, thereby causing a problem of being incapable of making smooth fine adjustment easy.
In order to solve various problems in the above-mentioned prior art, the present invention is intended to facilitate tilt adjustment work for adjusting the movement face of the optical pickup so as to be parallel with the recording face of the optical disk and to provide an optical disk apparatus being high in reliability and capable of meeting the needs for higher speed, larger capacity and lower profile. Furthermore, the present invention is intended to make the above-mentioned adjustment work by using the tilt mechanism easy and to provide a height adjustment device capable of easily fine-adjusting the distance between the chassis and the sub chassis.